The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to methods of self-aligned multiple patterning.
A back-end-of-line interconnect structure may be used to connect device structures, which were fabricated on a substrate during front-end-of-line processing, with each other and with the environment external to the chip. Self-aligned patterning processes used to form an interconnect structure involve linear mandrels acting as sacrificial features that establish a feature pitch. Non-mandrel lines are arranged as linear spaces between sidewall spacers that are formed adjacent to the sidewalls of the mandrels. After the mandrels are pulled to define mandrel lines, the sidewall spacers are used as an etch mask to etch a pattern predicated on the mandrel lines and the non-mandrel lines into an underlying hardmask. The pattern is subsequently transferred from the hardmask to an interlayer dielectric layer as trenches in which the interconnects are formed.
Mandrel cuts may be formed in the mandrels in order to section the mandrels and define discontinuities between the different sections. Non-mandrel cuts may also be formed along non-mandrel lines and may include portions of the spacer material used to form the sidewall spacers. The mandrel cuts and non-mandrel cuts are included in the pattern that is transferred to the hardmask and subsequently transferred from the hardmask to form the trenches in the interlayer dielectric layer. The mandrel cuts and non-mandrel cuts appear in the interconnect structure as adjacent interconnects that are spaced apart at their tips with a tip-to-tip spacing related to the dimension of the discontinuity.
The tip-to-tip spacing for the sections of a cut mandrel is limited to a distance equal to twice the thickness of the sidewall spacers. If the tip-to-tip spacing is greater than this distance, the sidewalls spacers do not merge between the tips of the sections of the mandrel, which results in incomplete filling of the mandrel cut. Transverse to the length of the cut mandrel, the mandrel cut is arranged in the pattern laterally between non-mandrel lines that flank the cut mandrel line. The result of the incomplete filling can be a conductive link shorting interconnects formed using the non-mandrel lines flanking the mandrel cut.
Even if the filling of the mandrel cut is complete, the wrapping of the sidewall spacers about the tips of the sections of the cut mandrel may introduce notches or indents at the side edges of the merged sidewall spacers. These notches or indents appear in the interconnect structure as kinks that project from the side edges of wires formed using the non-mandrel lines flanking the mandrel cut. The proximity of these kinks to each other may also result in shorting.
Improved methods of self-aligned multiple patterning are therefore needed.